1. Field of the Invention
This invention relates to a caster attached to a movable body to facilitate a change in the direction of movement of said body.
2. Description of the Prior Art
Casters are attached to a carrying unit or a body to be moved, such as a baby carriage for facilitating changing the movement direction.
FIG. 15 is a diagrammatic view showing a baby carriage of the type in which the push rod can be switched between two states, one for the face-to-back push mode and the other for the face-to-face push mode, wherein the front wheels are swivelable by casters. The baby carriage 1 shown comprises a pair of right and left front legs 3 rotatably supporting front wheels 2 at their lower ends through an axle 6, a pair of right and left rear legs 5 rotatably supporting rear wheels 4 at their lower ends through an axle 7, and a push rod 10. The push rod is installed in a pivotable or hingeable manner so that it can be switched between two states, one for the face-to-back push mode and the other for the face-to-face push mode. The position shown in solid lines in FIG. 15 corresponds to the face-to-back push mode of the push rod 10, while the dash-dotted line position corresponds to the face-to-face push mode of the push rod 10.
A caster 8 is attached to the lower end of each front leg 3. The caster 8 is turnable around the axis of rotation 9 and rotatably supports the front wheel 2 through the axle 6 which extends horizontally at a position horizontally spaced from the axis of rotation 9.
In the case where the baby carriage is moved on a flat road in the face-to-back push mode, the axle 6 for the front wheels 3 is positioned rearwardly of the axis of rotation 9 of the caster with respect to the direction of travel. FIG. 16 is a plan view diagrammatically showing the positional relationship of the two front wheels 2 and two rear wheels 4 and the directional orientation of the wheels with respect to the direction of travel. When the baby carriage 1 is moving straight in the face-to-back push mode, the two front wheels 2 and two rear wheels 4 are arranged in parallel to the direction of travel, as shown in FIG. 16. When it is desired to change the direction of the baby carriage 1, the casters 8 suitably swivel for facilitating the change of direction. Thus, the provision of casters 8 on the baby carriage 1 results in an improved operability.
The operation or switching of the mode shown in FIG. 15 to the face-to-face push mode and moving the baby carriage 1 will now be described. When the push rod 10 is switched to the face-to-face push mode as shown in phantom lines in FIG. 15 and the baby carriage is moved, the casters 8 are swiveled through 180 degrees and the front wheels 2 assume the dash-dotted line position. In this state, the axle 6 for the front wheels 2 is positioned rearwardly of the axis of rotation 9 of the casters 8 with respect to the direction of travel. Therefore, when the baby carriage 1 is moving straight, the pair of front wheels are parallel with respect to the direction of travel, as shown in FIG. 16.
When the baby carriage 1 is moved on a flat road, the casters 8 swivel as required, increasing the operability of the baby carriage 1. However, when the baby carriage is moved on a bad road, the swiveling action of the casters 8 does not improve the operability of the baby carriage 1, contrary to the expectation. Thus, such a baby carriage is generally provided with locking means for inhibiting the swiveling action of casters 8 as required.
However, with the casters 8 left locked, the user may sometimes forget to unlock them. In that case, the following problem arises. For example, suppose that the push rod 10 is in the face-to-back push mode and that the baby carriage 1 is being moved with the casters 8 in the locked position. Also suppose that the push rod 10 is changed to the face-to-face push mode without unlocking the casters 8. When the baby carriage 1 is moved under these conditions, the baby carriage is in a state in which it is very hard to push.
That is, as shown in FIG. 17, the axle 6 for the front wheels 2 is positioned forwardly of the axis of rotation 9 of the casters 8 with respect to the direction of travel. Even when the swiveling action of the casters 8 is inhibited by the locking means, there is still some play. Thus, if the baby carriage 1 is moved in the state shown in FIG. 17, the pair of front wheels 2 will swivel at random, as shown in FIG. 18. When the pair of front wheels 2 assumes a slanted position as shown in solid or dotted lines in FIG. 18, the front wheels 2 act as brakes, making it more difficult to push the baby carriage 1.